Insulin binding to its receptor triggers autophosphorylation of tyrosine residues. What is the IMMEDIATE downstream signaling molecule phosphorylated by the activated insulin receptor tyrosine kinase?
- A Phospholipase C-beta
- B Adenylyl cyclase
- C Insulin receptor substrate-1 (IRS-1) ✓
- D Protein kinase A (PKA)
Correct answer: C. Insulin receptor substrate-1 (IRS-1)
Explanation
The insulin receptor is a receptor tyrosine kinase. Upon insulin binding, the receptor undergoes conformational change, trans-autophosphorylates tyrosine residues in its cytoplasmic domain, and then phosphorylates IRS-1 (insulin receptor substrate-1) on multiple tyrosine residues. Phospho-IRS-1 then recruits PI3K (via p85 regulatory subunit), leading to PIP3 generation and downstream Akt/PKB activation for glucose transport. PLC-beta is coupled to Gq-linked receptors, not RTKs.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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